CVE-2026-99223 in Linux
Summary
by MITRE • 11/02/2026
In the Linux kernel, the following vulnerability has been resolved:
keys: make keyring indexes independent of kernel addresses
KEYCTL_READ returns the serial numbers in a keyring in associative-array traversal order. The first word of the index is a public, deterministic hash of the type pointer, domain pointer and description. An unprivileged user can therefore insert keys with known descriptions, predict their order for each possible KASLR slide, and recover the kernel image address. On an x86-64 build with 16 MiB alignment, 45 user keys suffice to distinguish the candidate slides.
Remove the addresses from the whole index, not just its first hash word. Assign each key type and domain a nonzero 64-bit ID and hash those IDs and the description with a once-initialized SipHash key. Use the full IDs in the later index chunks as well. Truncating or hashing the IDs there would lose the guarantee that distinct type/domain/description tuples have a differing index bit.
Allocate IDs lazily since private key types need not be registered. Cache them in the index key so tree walks and copies of an existing index do not need to dereference a type descriptor that may have been unregistered. Keep the 32-bit chunk layout and diff_objects() bit offsets consistent, and retain the separate root slot for keyrings used by recursive search. The key comparison, permissions and userspace data format are unchanged; only the address-dependent in-memory ordering is replaced.
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Analysis
by VulDB Data Team • 11/02/2026
The Linux kernel contained a critical information disclosure vulnerability within its key management subsystem that allowed unprivileged local users to bypass Kernel Address Space Layout Randomization (KASLR). The flaw originated from the implementation of KEYCTL_READ, which returns serial numbers for keys in a keyring based on associative-array traversal order. This ordering was determined by an index where the first word served as a public hash derived directly from kernel memory addresses, specifically the type pointer, domain pointer, and description string. Because these pointers are part of the kernel's virtual address space, their values change with each boot due to KASLR randomization. However, since the hash function used was deterministic and exposed through the user-space API, an attacker could exploit this predictability to reverse-engineer the current memory layout.
An unprivileged user could insert a controlled number of keys with known descriptions into a keyring and observe their resulting serial numbers upon retrieval. By analyzing the traversal order against potential KASLR slide values, the attacker could narrow down the possible kernel image addresses. Research indicated that on x86-64 systems with 16 MiB alignment granularity, inserting approximately forty-five user keys was sufficient to distinguish between candidate slides and effectively recover the base address of the kernel image. This breach undermines a primary defense mechanism against exploitation of other vulnerabilities, as knowing the kernel's location allows an attacker to locate gadgets for return-oriented programming or directly patch kernel structures during privilege escalation attacks.
To remediate this issue, developers modified the keyring indexing logic to completely decouple it from volatile kernel memory addresses. The solution involved assigning each unique key type and domain a persistent, nonzero sixty-four-bit identifier that remains constant across reboots rather than relying on ephemical pointer values. These identifiers are hashed together with the description using SipHash, which utilizes a once-initialized secret key added to prevent external prediction of hash collisions or orderings. This approach ensures that while the internal ordering may still vary based on input data, it no longer correlates with kernel memory layout, thereby neutralizing the side-channel used for KASLR bypassing.
The implementation also introduced lazy allocation for these identifiers since private key types do not require formal registration in all contexts. These IDs are cached within the index keys themselves to optimize performance during tree walks and when copying existing indexes, avoiding the need to dereference type descriptors that might have been unregistered or unloaded. The change preserved backward compatibility by maintaining the thirty-two-bit chunk layout and diff_objects bit offsets used for comparisons, as well as retaining separate root slots for keyrings involved in recursive searches. Crucially, while the internal memory ordering changed, the user-space data format, permission checks, and comparison logic remained unchanged to prevent breaking existing applications relying on KEYCTL_READ behavior.
From a security standards perspective, this vulnerability is classified under CWE-200 as an Information Exposure issue, specifically involving sensitive information leakage through side channels or predictable outputs that reveal internal system states. In the context of the MITRE ATT&CK framework for enterprise security, this flaw facilitates Discovery techniques related to System Information Discovery and potentially Defense Evasion by allowing attackers to bypass KASLR protections which are categorized under Anti-Bypassing Techniques. The mitigation aligns with best practices for secure coding that emphasize minimizing information leakage through APIs and ensuring that internal data structures do not inadvertently expose sensitive runtime state such as memory addresses.
Organizations running affected Linux kernel versions should apply the relevant security patches to restore the integrity of their KASLR implementation. Administrators must ensure that key management subsystems are updated, particularly in environments where unprivileged users have access to create keys within shared or user-specific keyrings. Continuous monitoring for unusual patterns in key creation and retrieval operations can help detect attempts to exploit similar information disclosure vectors before they lead to full system compromise. Maintaining up-to-date kernel versions remains the most effective strategy against such low-level memory layout exploitation techniques.